This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 2002-285078 filed in Japan on Sep. 30, 2002, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to projection-type display apparatuses capable of adjusting projection illumination.
2. Description of the Related Art
Projection TVs, which project and display images, are well known as one example of video apparatuses that realize largescreen TVs. Among projection TVs, there are two typical types, those that magnify and project CRT images and those that utilize light valves such as liquid crystal panels. While the former CRT-type projection TVs have a technical problem that picture quality technically contradicts picture luminance, the latter light-valve-type projection TVs have recently been developed so as to overcome the technical problem of the former CRT-type projection TVs. The light-valve-type projection TVs have an essential advantage in compatibility between picture quality and picture luminance since they have, as systems independent of each other, a light source, and light valves for forming images. However, in comparison with CRT-type projection TVs, the light-valve-type projections TVs have, because of light leakage, disadvantages in the contrast, especially display of black color. For instance, there has been a problem that, since in video images in movies and the like which contain many dark scenes, black level cannot be displayed in high contrast, the images appear to have background luminance in their nominally black regions, which spoils the viewer's sense of being present.
To cope with these problems, projectors utilizing a mechanical light shutter for controlling the amount of light which illuminates the light valve have been proposed (see, e.g., Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-23106 (p. 4-5, FIGS. 6-10) and Patent Document 2: Japanese Laid-Open Patent Publication No. 2002-90705 (p. 5-6, FIGS. 6-13)).
FIG. 12 is a plan view illustrating a projector described in Patent Documents 1 and 2. The projector shown in FIG. 12 is constituted from three principal parts including a light source unit 100, an illumination-optics unit 110 and a projection lens 120. Among them the illumination-optics unit 110 includes an integrator-optics system 111 and a color-separation/color-composition system 109. The integrator-optics system 111 includes a first lens array 112, a second lens array 113, a light shade 114 which acts as a light shutter, a polarization-conversion element 115 and a superposition lens 116. In FIG. 13, the configuration of the second lens array 113, the light shade 114, the polarization-conversion element array 115 and the superposition lens 116 is shown.
The light source unit 100 is provided with a light source lamp 101 and a concave mirror 102, radial light rays emitted from the light source lamp 101 are reflected by the concave mirror 102, and then emitted toward the first lens array 112 as approximately parallel light beams. The first lens array 112 has a matrix arrangement of a plurality of microlenses rectangular in contour, separating light emitted from the light source unit 100 into a plurality of partial light beams. The second lens array 113, being constituted from as many microlenses as those constituting the first lens array 112, functions to guide the plurality of partial light beams emitted from the first lens array 112 in such a way that the plurality of partial light beams is approximately condensed onto the polarization-separation element of the polarization-conversion element array 115. The polarization-conversion element array 115 is constituted from the polarization-separation element, which separates light emitted from the second lens array 113 into an S-polarization component and a P-polarization component, and a λ/2 phase difference plate that converts the polarization direction, and emits linearly polarized light by converting the polarization direction of an incident light beam.
The light shade 114 as a light shutter is arranged between the second lens array 113 and the polarization-conversion element array 115. The light shade 114, arranged opposite the incident light plane of the polarization-conversion element array 115, is a tabular body formed with alternating light reflection portions 117 that shut out light and have approximately the same width as that of the incident light and aperture portions 118 that allow light to pass through, as shown in FIG. 14. The light shade 114 is formed, in combination with a drive mechanism 119, so that the surface constituted from the light reflection portions 117 and the aperture portions 118 shifts in parallel to the incident light plane of the polarization-conversion element array 115 (X direction in FIG. 14), resulting in the incident light plane of the polarization-conversion element array 115 being openable and closable. That is, the amount of light entering the polarization-conversion element array 115 can be adjusted by shifting the light shade 114 in parallel. Since the polarization-conversion element array 115 is arranged just or proximately on the position where arc images of the light source form, the first lens array 112 is approximately in optically conjugate relationship with the incident pupil of the projection lens 120. This means that, even when light is shut out by the light shade 114 in the vicinity of the polarization-conversion element array 115, adjustment of brightness can be carried out without causing illumination non-uniformity, which is the same effect as the case with stopping-down the projection lens 120.
The foregoing method for adjusting the amount of light can raise the contrast of a displayed image and, especially, can be averted the problem that when a projected screen has a small size, background luminance in nominally black regions of the image makes the image brighter than necessary and the image is difficult to be watched.